What was found
(CAN) NOSE LANDING GEAR FAILED TO EXTEND WHEN SELECTED, NOSE GEAR STOPPED APPROX. AT HALF EXTENSION, LT & RT MAIN GEAR DOWN AND LOCKED, AT TOUCH DOWN NOSE GEAR COLLAPSED. FAILURE CAUSE BY AFT NOSE GEAR DRIVE CHAIN FAILURE P/N 50-820010-17 THE WRITER WILL CONTINUE TO DETERMINE CAUSE FOR THIS FAILURE AND WILL ADVISE AFTER FURTHER INVESTIGATION FOUND SEIZED BEARING P/N R12ZZ, INSTALLED IN BEARING ASSY.50-820140-3 CAUSING UNDO STRAIN/LOAD ON CHAINS.